A pneumotoxin, 4-ipomeanol, is currently being tested in humans as a therapeutic agent for the treatment of lung cancer. The rationale for its use is based on the fact that 4-ipomeanol undergoes activation by an isozyme of cytochrome P-450 to a reactive metabolite that causes destruction of pneumocytes. It appears now that an isozyme of cytochrome P-450 in rat lung responsible for the activation of 4-ipomeanol is present not only in lung but also in kidney of mouse. Interestingly the activity of the enzyme in mouse kidney microsomes is dependent on androgens. The very low level activity of the enzyme present in female mouse kidney was markedly increased by the treatment of mice with testosterone propionate.